The present invention relates to a gas turbine cooling blade capable of blowing deposits away and carrying out effective cooling operations.
FIG. 4 is a sectional view showing the cooling structure of a conventional gas turbine hollow stator blade. A hollow stator blade 11 is formed integrally with inside and outside shrouds (not shown in the Figure) by means of precision molding. Within the hollow stator blade 11 is installed an insert 13 having a plurality of cooling holes 12, and cooling air flows into it from the outside shroud. As shown by the arrows in the Figure, the cooling air flows out of the hole of the insert 13 and is brought into collision with the inner wall of the hollow stator blade 11 where impingement cooling is carried out, and the cooling air thus flows into a hollow chamber A formed between the insert 13 and the hollow stator blade 11.
The stator blade is then cooled while the cooling air flows toward the rear edge of the blade. A part of the cooling air flows out of a film cooling hole 14 along the blade profile and thereby the blade surface is film-cooled. The blade rear edge, including a pinfin 16, is convection-cooled by the cooling air flowing out of a slit 15 therein. Further, on a blade front edge thus is exposed most to high-temperature gas, a blade front edge part film cooling hole 18, called a shower head, is provided.
When the gas turbine cooling blade of this conventional type is used while burning heavy oil, etc., as described below, deposits 17 get stuck to a blade belly part where the flow speed is relatively slow, clogging the film cooling hole 14. These deposits are oxides made of such corrosive components as S(sulfur), Na(sodium) and the like included in fuels and Ca(calcium), Fe(iron), Si(silicon) and others included in intake air. They become solidified and stuck to the cooled blade surface when they are brought into contact therewith, though they are melted in an area of high-temperature gas at the front stage of the gas turbine, and they tend to stick more to the blade belly part where the flow speed is relatively slow.
In the case where the gas turbine cooling blade having the cooling structure described above is used for a gas turbine operated by burning, for example, crude oil and heavy oil other than such standard fuels as kerosene, gas oil, naphtha and the like, because many ashes and residual carbons are contained in heavy oil, deposits accumulate on the belly side of the turbine blade, and thereby the cooling performance of the air-cooling blade is greatly reduced within a short period of time. Consequently, high-temperature corrosion is generated.